Re: [Xen-users] Networking Help - Routed Configuration with NAT - How to get Dom0 to NAT its own connections

[Pierre-Alain RIVIERE <pariviere@xxxxxxxx>]

Hi,

Sending mail from dom0 to domU involves source IP is dom0 one. Your 
configuration seems to use source IP and the NAT rules only specifies 
10.0.66.66, which is your domU IP. This rules can't be succeed when 
sending mail from domU to dom0. If your redirect rules is built the same 
way, it also does not work.
By the way, why use dom0 as router and make it available via public IP? 
I think it should be preferable to make directly your domU available via 
its public IP. In this cas no need to NAT or whatever and your domU do 
not handle incoming IP connections.
Jason wrote:
> Hi,
>
> After loads of trial and error, I have managed to get a pretty workable network 
> configuration set up:
>
> The server is allocated public ips in xxx.xxx.xxx.192/29. Dom0 is bound to 
> xxx.xxx.xxx.194-198
>
> Xend is configured to use the default network-route and vif-route scripts.
>
> DomU is to be mail server responding on IP xxx.xxx.xxx.198
>
> DomU network configuration is vif = [ 'ip=10.0.66.66' ]
>
> Set up NAT:
> iptables -t nat -A POSTROUTING -o eth0 -j SNAT -s 10.0.66.66 --to 
> xxx.xxx.xxx.198
> iptables -t nat -A PREROUTING -i eth0 --dport 25 -j DNAT -d xxx.xxx.xxx.198 
> --to 10.0.66.66
>
> At this stage everything works great, Except for one thing:
>
> When Dom0 tries to send mail to the DomU - i.e. connecting to 
> xxx.xxx.xxx.198:25 from Dom0, it tries to connect to itself - not DomU!
>
> So in essence it is not NATing its own connections. I figured it is because it 
> is configured to listen to xxx.xxx.xxx.198 (thus skipping iptables?) - so I 
> unbound it from xxx.xxx.xxx.198 and then it seemed to work fine - for a while - 
> until I think the router flushes its ARP cache. So then I started to read up on 
> ARP and proxy arp etc... but still am not making much headway.
>
> I would be grateful to anybody able to shed any light / hints on this!
>   

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